I just came back from a 5700 mile trip in an '08 386 Pete with a C-15 as the engine

The engine is a CPX, and the dash readout gives the engine model # as EMY 2007 C. I have the full serial number if needed.

With 34k in the box, driving around 67 MPH, turning 1350 rpm, it got 3.6 MPG. Across I-40 to CA with 40k it got 3.2 MPG. Coming back along 10 & 20 with 15k in the box, a tail wind most of the time, and alternating between 67 and 70 MPH it averaged 4.2 MPG, turning 1440 RPM at 70 MPH. There was no difference in fuel mileage between 67 and 70 MPH, and only a couple tenths or so at 63.

There are no codes according to the display, which constantly checks, and does a complete system check upon startup. The Regen Required light came on three times to level one, but each time it did a rolling regen, and within a few minutes it cleared right up.

This truck was ran team, so almost no idling, and the mileages were fillup to fillup legs, calculated according to the computer readout. I also did a manual check that confirmed the readout was spot on each time I checked it.

The engine plate reades 475 HP max, but it seems less than that.

Is this normal, or is something wrong. What, if anything can be done to a company truck with this engine that will help. Will the fuel temp wire even work on these DPF engines.

Any help will be appreciated.

What was the engine running temp??

That mileage seems awfully low for that engine.

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It ran 195-200 all the time, oil temp about 205.

I kept the MPG readout on instant and average. As soon as the throttle was touched the instant reading would drop to 3.2 or less. I saw it at 1.5 on one hill. Full throttle on a slight hill would net 2.6.

The company has about 20 of these things, and I think they are killing them with the fuel mileage.

Both CAT and Cummins had issues with auto-regen.
You never had to manually regen...
When the Regen light went on did the power seem to drop?

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No power drop at all. The power should not drop until lever 3 or 4. The regen worked great usually. I never had to do a manual regen.

The only time I knew it was happening is in town I could smell the burnoff, and ocassionally the high exhaust temp reading would come on, but this only happened when stopped, or moving very slowly.

You were running at 1440 at 70mph....
What kind of tranny and rears does the truck have?
These newer CATS are supposed to run at 1200 Rpms which is peak torque from what I have read.
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What if you ran it at 1200, would that dog the engine?

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I don't know if 1200 would dog the engine, but it sure would be slow. It starts dropping off pretty fast around 1100, so it would be hard to run at 1200. I can't get it to turn over 1700 in any gear, so it is cut back some.

I usually shift around 1400 in the low side up through 7th, about 1500 into 8th, and around 15-1600 in 9th to 10th shifts.

The trans is a 10 spd overdrive, and the rears I think are 3.36, at most 3.25, but I think 3.36 is it. 22.5 lp tires.

Yeah....
these new engines are supposed to run at lower Rpms than the older ones.
I remember when I started driving that you ran at 1800, then the ECM engines came out and then you ran at 1600.
I worked with a guy who bought a 2007 dump with a C15 and a full auto. He ran it at 1100 and that was its "sweet spot" loaded or empty; flat or grade.

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Obama and Company: Step aside and let the adults take Charge.......Playtime is over.....

If the rears are 3.36, which I am sure they are, them 1200 would be 57 MPH. These trucks are supposed to run 5200-5800 miles per week with somewhat time sensitive freight. I sure would hate to do that at 57.

Apparently MPG isn't an issue with them right now.
You can't hurt the engine by running it at a higher rpms you said you were running at.

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Obama and Company: Step aside and let the adults take Charge.......Playtime is over.....